Answer:
The probability that a person adds both sugar and honey is 0.04.
Explanation:
P(H) means "probability that a random person adds honey"
P(S) means "probability that a random person adds sugar"
P(H or S) means "probability that a random person adds AT LEAST ONE OUT OF honey and sugar"
P(H and S) means "probability that a random person adds BOTH honey and sugar"
We can simplify it as "percentage of people who add" instead of "probability that a random person adds", and then it should be clear to us that
P(H or S) = P(H) + P(S) - P(H and S)
The equation comes from the face that if we want to compute percentage of people who add at least one sweetener, we can sum people who add honey and people who add sugar, but we would have counted people who use both TWICE, so we can correct by subtracting. As follows:
P(H and S) = P(H) + P(S) - P(H or S)
P(H and S) = 0.15 + 0.68 - 0.79 = 0.83 - 0.79 = 0.04
So the probability that a person adds both sugar and honey is 0.04.